Neither document actually defines what the fragment identifier
*means*: this is presumably left to the HTML spec.
RFC 1808 seems to disallow spaces in #fragments. I think the choices
are:
1) HTML disallows spaces in anchors
2) RFC 1808 is wrong, or doesn't apply to HTML. Spaces are allowed in anchor references
3) Spaces aren't allowed in #fragment identifiers, are encoded, but
are allowed as name references.
Personally I prefer (1).